Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting a frame on the basis of a sounding procedure.
Related Art
A wireless local area network (WLAN) system may support a downlink multi user-multiple input multiple output (MU-MIMO) transmission method for a higher throughput. An access point (AP) may simultaneously transmit data frames to at least one or more stations (STAs) which are MIMO-paired through a downlink. In the legacy WLAN system, the maximum number of paired STAs may be 4, and when the maximum number of spatial streams is 8, up to 4 spatial streams may be allocated to each STA.
For example, in the WLAN system, the AP may simultaneously transmit data to an STA group including at least one or more STAs among a plurality of STAs associated with the AP. In a WLAN system in which the AP not only performs MU-MIMO transmission to the STAs but also supports a tunneled direct link setup (TDLS) or direct link setup (DLS) and a mesh network, an STA which intends to transmit data may transmit a PLCP protocol data unit (PPDU) to the plurality of STAs by using the MU-MIMO transmission scheme. In case of using MU-MIMO, data to be transmitted to each STA may be transmitted through a different spatial stream.